1. Field of the Invention
The present invention relates to an electromagnetic wave detecting element. In particular, the present invention relates to an electromagnetic wave detecting element that uses a TFT active matrix substrate that detects an image and at which sensor portions are provided in correspondence with respective intersection portions of plural scan lines and plural signal lines that are disposed so as to intersect one another.
2. Description of the Related Art
Radiation image detection devices such as FPDs (flat panel detectors), in which an X-ray sensitive layer is disposed on a TFT (thin film transistor) active matrix substrate and that can convert X-ray information directly into digital data, and the like, have been put into practice in recent years. As compared with a conventional imaging plate, an image can be confirmed immediately at an FPD. Further, the FPD has the advantage that video images as well can be confirmed. Therefore, the popularization of FPDs has advanced rapidly.
Various types of radiation image detection devices are proposed. For example, there is a direct-conversion-type radiation image detection device that converts radiation directly into charges and accumulates the charges. Moreover, there is an indirect-conversion-type radiation image detection device that once converts radiation into light at a scintillator of CsI:Tl, GOS (Gd2O2S:Tb), or the like, and, at semiconductor layer, converts the converted light into charges and accumulates the charges (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2000-137080).
As an example, a plan view showing the structure of one pixel unit of an electromagnetic wave detecting element 10′ that is used in an indirect-conversion-type radiation image detection device, is shown in FIG. 12. Further, a cross-sectional view along line A-A of FIG. 12 is shown in FIG. 13.
As shown in FIG. 12, sensor portions 103′ are provided at the electromagnetic wave detecting element 10′, in correspondence with the respective intersection portions of plural scan lines 101′ and plural signal lines 3′ that are disposed so as to intersect one another.
As shown in FIG. 13, the sensor portion 103′ includes a semiconductor layer 6′, an upper electrode 7′, and a lower electrode 14′. The semiconductor layer 6′ generates charges due to light being illuminated. The upper electrode 7′ is formed by a light-transmissive, electrically-conductive member at an illumination surface side of the semiconductor layer 6′ at which light is illuminated, and applies bias voltage to the semiconductor layer 6′. The lower electrode 14′ is formed at the light non-illumination surface side of the semiconductor layer 6′, and collects charges that are generated at the semiconductor layer 6′.
At the electromagnetic wave detecting element 10′, common electrode lines 25′, that supply bias voltage to the upper electrodes 7′, are disposed at the upper layer of the semiconductor layer 6′. The resistance of the common electrode lines 25′ must be made to be low in order to supply charges. Therefore, the common electrode lines 25′ are formed by using a low-resistance wiring material of Al or Cu, or material including Al or Cu.
U.S. Pat. No. 5,777,355 discloses a technique of connecting respective upper electrodes that are formed from transparent, electrically-conductive members, so as to have them function also as common electrode lines.
However, as shown in FIG. 13, if the common electrode lines 25′ are disposed at the illumination surface sides of the semiconductor layer 6′, contact portions 27′ are needed in order to connect the common electrode lines 25′ and the upper electrodes 7′. However, the efficiency of utilization of light decreases due to the contact portions 27′.
Contact holes 27A′ are disposed at the centers of the contact portions 27′. Further, in order to keep the contact resistance between the common electrode lines 25′ and the upper electrodes 7′ low, and because of the fabrication yield of the photolithographic process at the time of manufacturing the electromagnetic wave detecting element 10′, the size of the contact holes 27A′ must be greater than or equal to 4×4 μm, and preferably greater than or equal to 8×8 μm. Moreover, at the contact portions 27′, contact pads 27B′ that electrically connect the common electrode lines 25′ and the upper electrodes 7′ must be made to be larger than the contact holes 27A′. Therefore, the size of the contact portions 27′ must be greater than 10×10 μm, and preferably greater than or equal to 15×15 μm.
Here, by using the technique disclosed in aforementioned U.S. Pat. No. 5,777,355, the upper electrodes 7′, that are formed from transparent, electrically-conductive members, are respectively connected and made to function also as common electrode lines.
However, usually, the resistivity of a transparent, electrically-conductive member is large, and is 50 to 200 times that of a low-resistance wiring material. Therefore, if the upper electrodes 7′ are respectively connected and made to function also as common electrode lines, the wiring load (resistance, capacity) of the common electrode lines increases, and the desired response cannot be realized. Thus, the upper electrodes 7′ cannot be respectively connected and made to function also as common electrode lines.
The inventors propose a structure in which the common electrode lines 25′ are disposed at the electromagnetic wave irradiation surface downstream side of the semiconductor layer 6′.
As an example, FIG. 14 is a plan view showing the structure of one pixel unit of the electromagnetic wave detecting element 10′ at which the common electrode line 25′ is disposed at the electromagnetic wave irradiation surface downstream side of the semiconductor layer 6′. Further, a cross-sectional view along line A-A of FIG. 14 is shown in FIG. 15A, and a cross-sectional view along line B-B of FIG. 14 is shown in FIG. 15B.
In this structure, a deterioration in the light utilization efficiency due to the common electrode lines 25′ does not arise. However, in this structure, in order to apply bias voltage to the upper electrodes 7′ of the sensor portions 103′, contact portions 22′ are provided respectively at the sensor portions 103′ and electrically connect the common electrode lines 25′ and the upper electrodes 7′ of the respective sensor portions 103′. In particular, in this structure, as compared with conventional structures, the semiconductor layer 6′ cannot be disposed in vicinities of the contact portions 22′, and therefore, the light utilization efficiency decreases greatly.
Note that, in the above description, the efficiency of utilization of light is mentioned because light is the object of detection of the semiconductor layer 6′. However, the same holds as well in cases in which the object of detection is any type of electromagnetic waves such as ultraviolet rays or infrared rays.